1. Field of the Invention
This invention relates to a shuttle hook driver provided in sewing machines for reciprocating a shuttle hook linked to a full turn main shaft, and more particularly to such a shuttle hook driver reciprocating the shuttle hook about a horizontal shaft crossing a shaft center of the main shaft.
2. Description of the Related Art
In sewing machines, a main shaft is generally driven by a sewing machine motor so that a needle bar and a thread loop taker both linked to the main shaft are driven. A sewing needle is attached to a lower end of the needle bar. Upon drive of the needle bar and the thread loop taker, a needle thread having passed through an eye of the needle is caught by a loop seizing beak of the thread loop taker so that the needle thread is entangled with the bobbin thread, whereby a stitch is formed.
Shuttle hooks have widely been used as the above-mentioned thread loop taker. The shuttle hook is reciprocated about a horizontal shaft crossing a shaft center of the main shaft. The prior art has provided various types of drivers for driving the shuttle hook. FIG. 10 illustrates one of the conventional shuttle hook drivers. As shown, a body 100 of the sewing machine includes an arm 100a and a sewing bed 100b. A main shaft 102 extending leftward and rightward as viewed in FIG. 10 is provided in the arm 100a. A shuttle hook 110 is provided in the bed 100b to be reciprocated about a horizontal shaft crossing the center of rotation of the main shaft 102. A shuttle hook driver 101 comprises a cam 103 fitted with the main shaft 102 to be fixed thereto, a driven member 104 moved in a cam groove 103a of the cam 103, a link member 105 supported on the sewing machine body 100 via a shaft 105a having a distal end to which the driven member 104 is secured, a pinion 106 fixed to the shuttle hook 110, a rack member 108 having a rack 107 meshed with the pinion 106 and a left-hand end urged downward by a spring 120, and a horizontal arm 109 extending rightward from the rack member 108 and having a right-hand end rotatably connected to a lower end of the link member 105.
Upon drive of the main shaft 102 and the cam 103 by a sewing machine motor (not shown) in the direction of arrow A, the driven member 104 is moved in the cam groove 103a in the above-described shuttle hook driver 101. The link member 105 is then rocked about the shaft 105a so that the rack member 108 is reciprocated rightward and leftward together with the horizontal arm 109. As a result, the shuttle hook 110 is reciprocated about the horizontal shaft.
A needle bar 115 including a sewing needle 116 is provided on a left-hand end of the arm 100a. A crank 118 is secured on the left-hand end of the main shaft 102. A rocking member 119 is rotatably connected both to the needle bar 115 and to the crank 118. Accordingly, upon drive of the main shaft 102, its rotation is transmitted via the crank 118 and the rocking member 119 to the needle bar 115, so that the needle bar and accordingly, the needle 116 are reciprocated upward and downward. Japanese Laid-open Utility Model Registration Publication No. 61-67681 (1986) also discloses the construction similar to that shown in FIG. 10.
Japanese Patent No. 2684661 discloses another shuttle hook driver for sewing machines. The disclosed shuttle hook driver comprises a first gear fixed to a main shaft, a second gear rotatable about a horizontal shaft crossing the main shaft and meshed with the first gear in the crossing state, a first pulley provided in the bed of the body, a second pulley fixed to the shuttle hook, a timing belt extending between the first and second pulleys, and a crank mechanism including a vertically elongated rink member and converting rotation of the second gear to reciprocation of the first pulley.
Upon drive of the main shaft and the first gear by a sewing machine motor in the above-described shuttle hook driver, the first pulley is reciprocally rotated via the second gear and the link member. The reciprocation of the first pulley is transmitted via the timing belt to the second pulley, whereby the shuttle hook is reciprocated.
Japanese Laid-open Patent Publication No. 63-11194 (1985) discloses a shuttle hook driver for a belt-driven sewing machine. The disclosed shuttle hook driver comprises a driving pulley connected via a drive belt to an output shaft of a sewing machine motor, a first driven pulley for drive of a needle bar, a second driven pulley for drive of the shuttle hook, a timing belt extending between the driving pulley and the first and second driven pulleys, a plurality of idle pulleys guiding the timing belt, a pinion fixed to the shuttle hook, a rack member including a rack meshed with the pinion, and a crank mechanism for converting rotation of the second driven pulley to reciprocation of the rack member.
In the above-described shuttle hook driver, the second driven pulley is rotated via the timing belt upon drive of the sewing machine motor. The rack member is reciprocated by the crank mechanism. Consequently, the shuttle hook is reciprocated about the horizontal shaft via the rack and pinion.
The above-described conventional shuttle hook drivers have the following problems. In the shuttle hook driver 101 shown in FIG. 10, the rotation of the main shaft 102 is converted by the cam 103, the link member 105, etc. to the reciprocation. In this case, it is technically difficult to engage the driven member 104 provided on the link member 105 with the cam groove 103a of the cam 103 without gap therebetween. However, when engaging the cam groove 103a with some gap therebetween, the driven member 104 collides with an inner surface of the cam groove 103a during operation of the sewing machine, thereby producing a loud noise. Furthermore, the cam groove 103a needs to be accurately formed in the cam 103 so that the vertical movement of the needle 116 or the needle bar 115 is synchronized with the reciprocation of the shuttle hook 110. This results in an increase in the manufacturing cost of the sewing machine.
The link member 105 transmitting the driving force is vertically long. Accordingly, the link member 105 needs to be made of a material with high strength so as not to suffer an elastic deformation during operation of the sewing machine, and more particularly during a high speed operation thereof. This also increases the manufacturing cost of the sewing machine. Generally, vibration tends to occur when a full turn member is disposed in an upper interior of the sewing machine body. In the above-described conventional construction, the cam 103, which is a full turn member, is disposed in an upper interior of the body. Moreover, the cam 103 rocks the vertically long link member 105. As a result, the vibration increases during the operation of the sewing machine.
In Japanese Patent No. 2684661, the first and second gears transmit the rotation of the main shaft to the horizontal shaft crossing the main shaft. Rotation of the horizontal shaft is then converted by the link member to reciprocation. Transmitting the driving force by the use of a plurality of gears reduces a transmission efficiency. Furthermore, the rotation of the second gear delays relative to the rotation of the first gear when the first and second gears are not in an accurate mesh engagement with each other.
Also, in Japanese Patent No. 2684661, full turn members, that is, the first and second gears are disposed in the upper interior of the body, and the rotation is converted to the reciprocation via the vertically long link member by the second gear. This results in the same technical problem as that described above concerning the shuttle hook driver shown in FIG. 10.
In Japanese Laid-open Patent Publication No. 63-11194, the timing belt is long so as to require a plurality of idle pulleys guiding it. This complicates the construction of the shuttle hook driver. The long timing belt further results in a difficulty in an adjustment for the vertical movement of the needle bar in synchronism with the reciprocation of the shuttle hook.